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D is corrent because in order for a mortgage to be effective between the mortgagor (borrower) and mortgagee (lender), it must be signed only by the mortgagor.
A is incorrect because the mortgage must be recorded to be effective against subsequent third parties acquiring an interest in the property who had no knowledge of the existing mortgage. The mortgage need not be recorded to be effective against third parties who purchase with knowledge of the existing mortgage.
B is incorrect because the mortgage must be delivered to the mortgagee to be effective.
C is incorrect because the recording of a mortgage has no effect on the rights of the mortgagee against the mortgagor. The purpose of recording the mortgage is to give constructive notice to third parties acquiring an interest in the property that the property is subject to an existing mortgage.